1. Yes the oe mk2 system is pretty complex with vac lines everywhere double function relay etc etc mk3 on mostly handled by the fcm and back to simple.cable.setup for the flaps. The MK2 and mk3 recirc flaps are both vacuum though so you could use a MK2 blower housing though this may not work depending on the AC rad inside Vs pipes etc so see how you go. 2. Inside the car in a nutshell depends what setup you want to use, and how much effort you want to put in. If you wanted mk3/4 and didn't care about it looking non factory you just fit an AC and recirc button same as the aftermarket installers would fit to the mk2 back in the day. If you were a bit more handy you could hook up micro switches to be pressed at the right point by the MK2 sliders like you say. Mk3/4 controlls are larger than MK2 so it's more effort to fit, but it can be done (see my MK4 climatrpnic -> mk2 thread) Not really sure on longevity but I've not heard anyone complain? 3. Up to you really, main difference is the mk3 fcm has fuses built in and the MK4 does not (fused by battery box) either could be made to work either way I would pick whichever is less work in your situation 4. Lines is the one thing I've not managed to play with, as even after all these years I haven't put the compressor.side of things into my MK2
I'm just trying to track down the wiring I stripped out of the MK3. Stuff is all over the place pending a house move.
I have a problem with mk3 ac fitted on my jetta. Recently put a new compressor on, but on colder days with blower fan on low, after some time the compressor starts to make a whine sound, as if a bearing is bad, and on a longer drive the heater box got so cold that formed condensation and leaked on the floor mat. The heater box has the original isolating material on, and the refrigerant capacity is 800 but put 750gr. Problem is it cools too much, as i saw once some ice on the thick pipe from expansion valve. I am curious to know what pressure is on low side when the whine is heard from compressor. Old compressor never had these problems, and only replaced because it had a small leak on the shaft.
On my Mk2 there is a low temp cut out thermo switch which is inside the evaporator housing in the cabin. Does your car not have this? Shuts down compressor
Do you have high and low pressure cut out switches to protect the system. Is your drier quite old/been exposed to damp? Is it new(ish). A faulty drier can sometimes lead to refrigerant icing up rather than moving along the system
The refrigerant which is already too cold is not warmed up at lower fan speed due to the fan not passing enough warmer air over the evaporator fins. The compressor is working too hard due to freezing. This is what is making the noise from the compressor.
There is a thermo switch outside for disabling ac winter time, mk3 manual ac have it. Drier filter was new when I fitted ac some time ago and always had refrigerant. First thing i will try is add some refrigerant 50-100gr and see how it performs, and work from there. Last thing is adding a thermo switch on evaporator, maybe replace expansion valve before.
yeah the mk3 doesnt (usually) have a thermoswitch on the ac rad block head thing, just the one in the scuttle plus 4 pin pressure switch. mk3 abf also have a thermoswitch in the coolant housing side of the head
